The present invention relates to the measurement of the properties of steam, and more particularly to the on-line measurement of steam quality.
Accurate and reliable on-line measurement of steam quality is desired at a number of locations in power plants an petro chemical operations to monitor equipment performance, perform heat balances, and the like. The standard technique for determining steam quality utilizes throttling calorimeters and throttling separating calorimeters, in accordance with ASME Power Test Code 19.11 - 1970 Part II. These standard devices are not very suitable for continuous on-line measurement of steam quality. One of the disadvantages of throttling calorimeters and throttling separation calorimeters, is that the steam is normally discharged to atmospheric pressure where the steam sample is required. Thus, these devices are not generally used as "on-line" monitoring devices.
Recently, devices have appeared commercially which rely on the determination of steam density as an on-line indication of steam quality. In at least some instances, such devices may not be stable at, for example, 200 psia, and at higher pressures, such as 600 psig, their accuracy is still course, e.g., approximately .+-.5%. One example is described in International Patent Application No. PCT/US87/0276
U.S. patent application No. 141,556 filed Jan. 7, 1988 now U.S. Pat. No. 4,833,688 describes another technique for measuring steam quality which has the capability of improved performance over known devices, but it requires the heating of a sampling vessel and the maintenance of a high degree of insulation around the heated vessel.